Important: The resources here are very old, and probably obsolete. You would be better off starting at the Firefox OS homepage.
Resources for App hackers, as generated from our workshops
Firefox OS Simulator
Firefox OS Simulator
https://developer.mozilla.org/en-US/docs/Tools/Firefox_OS_Simulator/
https://addons.mozilla.org/en-US/firefox/addon/firefox-os-simulator/
Developing/installing an app
Firefox OS Boilerplate App (work in progress)
https://github.com/robnyman/Firefox-OS-Boilerplate-App
http://robnyman.github.com/Firefox-OS-Boilerplate-App/
(clean basic version with Install button, Web Activities, WebAPI examples, optional offline support etc)
Code for version with packaged app:
https://github.com/robnyman/Firefox-OS-Boilerplate-App/tree/packaged-app
FxOSStub (template/design for an app with an Install button):
https://github.com/Jaxo/fxosstub
Recommended: host on your own server or through GitHub pages
(http://pages.github.com/). Example at http://robnyman.github.com/Firefox-OS-Boilerplate-App/
Mortar:
https://hacks.mozilla.org/2013/01/writing-web-apps-quickly-with-mortar/
Design patterns:
https://marketplace.firefox.com/developers/docs/patterns
Firefox OS Design Guidelines:
https://t.co/I9VaxvBu
droid@screen: http://blog.ribomation.com/droid-at-screen/
WebAPIs
WebAPIs in version 1:
https://wiki.mozilla.org/WebAPI
Documentation and their status for APIs:
https://developer.mozilla.org/en-US/docs/WebAPI/Doc_status
Robert's slides on Web APIs
http://www.slideshare.net/robnyman/web-apis-apps-mozilla-london
Writing (good) Webapps:
http://jlongster.github.com/writing-webapps/
Firefox Marketplace & Developer Hub
File a bug on Marketplace!
https://bugzilla.mozilla.org/enter_bug.cgi?product=Marketplace&component=General
Developer Hub
https://marketplace.firefox.com/developers/
WebApps mailing list
https://lists.mozilla.org/listinfo/dev-webapps
Marketplace Development Server (expect bugs!)
http://marketplace-dev.allizom.org/
Reference apps (Chrono, Face Value, Roller):
https://marketplace.firefox.com/developers/docs/apps/chrono
WebPayments
https://wiki.mozilla.org/WebAPI/WebPayment
https://wiki.mozilla.org/WebAPI/WebPaymentProvider
Pitfalls and helpers for mobile Web apps
Rob's slides on Pitfalls and Helpers
http://www.slideshare.net/robhawkes/mobile-app-development-pitfalls-helpers